1. Field of the Invention
This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of a suspension including a circuit trace constructed of circuit layers on opposite sides of a stainless steel layer, where the stainless steel layer have windows formed therein to allow passage of electric fields between the circuit layers.
2. Description of Related Art
Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit 100 includes a spinning magnetic disk 101 containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 to which a magnetic head slider (not shown) which defines a read/write head is mounted proximate a distal end of load beam 107. The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end nearest to base plate 12 (FIG. 2) which is swaged or otherwise mounted to an actuator arm. The “distal” end of a suspension or load beam is the end that is opposite the proximal end, i.e., the “distal” end is the cantilevered end.
Suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 108 that moves the suspension 105 arcuately in order to position the head slider over the correct data track on data disk 101 or other recording medium. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk's surface. The gimbal and the flexible circuit are typically part of the suspension called the flexure.
Circuit integrated suspension (CIS) and trace suspension assembly (TSA) are known technologies for manufacturing flexures. These flexures typically have wiring trace impedances in the 50 to 100 ohm range. The wiring trace, also called the circuit trace or flexible circuit, electrically connects the slider and PZT components to control circuitry (not shown) of the hard disk drive. One portion of the wiring trace runs from slider contacts near the distal end of the suspension to the proximal end of the suspension. Another portion of the wiring trace runs from the PZTs to the proximal end of the suspension.
FIG. 2 is a side sectional view of a portion of a prior art suspension including a flexure circuit 10. A supporting layer 12 such as a stainless steel layer is coated with a dielectric layer 14 such as polyimide; conductive signal traces 16 and 18 such as copper or copper alloy are metalized on the polyimide layer; and a cover coat or coverlayer 20 of an insulator such as polyimide is applied over the copper traces 16, 18 and the insulating dielectric layer 14.
Circuit traces manufactured using CIS and TSA flexure technologies can have trace impedances in the 40-50 ohm range and a circuit bandwidth of over 6 GHz. However, the spacing between traces and the ground layer that can be manufactured using these technologies is limited. Consequently, flexures manufactured using these technologies are not expected to be able to meet future hard disk drive requirements that call for an impedance of less than 30 ohms along with a bandwidth of over 6 GHz.
Known techniques such as the use of interleaved traces or stacked traces can achieve impedances below 50 ohms. For example, a stack trace design can be constructed by adding an additional layer on top of the first circuit layer. Such designs have significant bandwidth limitations, however. For example, simulations have indicated that the stack trace design may be limited to a bandwidth of less than 3 GHz. In addition, simulations have indicated that the interleave trace design may be limited to a bandwidth of less than 7 GHz. Consequently, interleave trace designs and stack trace designs are not an optimal choice for future hard disk drive designs, such as designs for suspensions for 3.5 inch disks, that call for an impedance below 50 ohms along with a bandwidth of 8 GHz for a circuit having a length of 50 mm.